The present invention relates to a compressible, thermally conductive interface foam product adapted to be disposed between two heat transfer surfaces, such as an electronic component and a heat sink, to provide a thermal pathway between the surfaces. The thermally conductive foam interface product comprises a layer of a cured elastomeric material having air-filled voids passing at least partially through the interface, and a thermally-conductive particulate filler dispersed in the cured product. A thermal management assembly comprising the interface product and the two heat transfer surfaces is also provided. Preferably, the interface material is a silicone pad which is coated, molded or extruded and filled with ceramic fillers, such as Al2O3 or BN particles.
Conventional circuit designs for modern electronic devices such as televisions, radios, computers, medical instruments, business machines, communications equipment, and the like have become increasingly complex. For example, integrated circuits have been manufactured for these and other devices which contain the equivalent of hundreds of thousands of transistors. Although the complexity of the designs has increased, the size of the devices has continued to shrink with improvements in the ability to manufacture smaller electronic components and to pack more of these components in an ever smaller area.
In recent years, electronic devices have become smaller and more densely packed. Designers and manufacturers are now facing the challenge of dissipating the heat generated in these devices using various thermal management systems. Thermal management has evolved to address the increased temperatures created within such electronic devices as a result of the increased processing speed and power of these devices. The new generation of electronic components squeeze more power into a smaller space; and hence the relative importance of thermal management within the overall product design continues to increase.
An integral part of a thermal design process is the selection of the optimal Thermal Interface Material (“TIM”) for a specific product application. New designs have been devised for thermal management to help dissipate the heat from electronic devices for further enhancing their performance. Other thermal management techniques utilize concepts such as a “cold plate”, or other heat sinks which can be easily mounted in the vicinity of the electronic components for heat dissipation. The heat sink may be a dedicated, thermally-conductive metal plate, or simply the chassis or circuit board of the device.
To improve the heat transfer efficiency through the interface, a pad or other layer of a thermally-conductive, electrically-insulating material often is interposed between the heat sink and electronic component to fill in any surface irregularities and eliminate air pockets. Initially employed for this purpose were materials such as a silicone grease or wax filled with a thermally-conductive filler such as aluminum oxide. Such materials usually are semi-liquid or solid at normal room temperature, but may liquefy or soften at elevated temperatures to flow and better conform to the irregularities of the interface surfaces.
The greases and waxes of the aforementioned types generally are not self-supporting or otherwise form-stable at room temperature, and are considered to be messy to apply to the interface surface of the heat sink or electronic component. Consequently, these materials are typically provided in the form of a film, which often is preferred for ease of handling, a substrate, a web, or other carrier which introduces another interface layer in or between the surfaces in which additional air pockets may be formed. Moreover, the use of such materials typically involves hand application or lay-up by the electronics assembler which increases manufacturing costs.
Alternatively, another approach is to substitute a cured, sheet-like material in place of the silicone grease or wax. Such materials may contain one or more thermally-conductive particulate fillers dispersed within a polymeric binder, and may be provided in the form of cured sheets, tapes, pads, films and foams. Typical binder materials include silicones, urethanes, thermoplastic rubbers, and other elastomers, with typical fillers including aluminum oxide, magnesium oxide, zinc oxide, boron nitride, and aluminum nitride.
Foamed materials offer enhanced thermal transfer for certain applications such as for electronic equipment and circuit boards. Various methods for making such foamed materials have been previously described in the patent literature. U.S. Pat. No. 2,604,663 discloses a method for forming internal voids in a molded rubber article by subjecting the mold to extreme temperature changes. U.S. Pat. No. 4,171,410 discloses elastomeric, conductive foam articles prepared by coating strands of a non-conductive foam with conductive particles, and compressing and heating the foam.
U.S. Pat. No. 6,033,506 describes a method for making a foam product from carbon pitch by alternatively heating and cooling the pitch in a mold in the presence of an inert fluid applied under pressure. U.S. Pat. No. 6,287,375 also describes a carbon foam product made from pitch which is thermally conductive due to the inclusion of a particulate, such as carbon fiber, in the foam. The foam is described as having a thermal conductivity of at least about 43 W/mK. See, also, U.S. Pat. No. 7,118,801, relating to a moldable heat conducting material formed from aerogel particles contained in a polytetrafluoroethylene binder, and having a thermal conductivity of less than about 25 mW/mK.
U.S. Pat. No. 7,208,192 discloses the application of a thermally and/or electrically conductive compound to fill a gap between a first and second surface. A supply of fluent, form-stable compound is provided as an admixture of a cured polymer gel component and a particulate filler component. The compound is dispensed from a nozzle under an applied pressure onto one of the surfaces which is contacted with the opposing surface to fill the gap there between. U.S. Pat. No. 6,784,363 illustrates a compressible gasket having a plurality of vias extending through the gasket. The gasket is provided with electrically conductive layers for EMI shielding.
The respective disclosures of each of the patents and patent applications listed above are incorporated by reference herein in their entireties.
In view of the variety of materials and applications currently used in thermal management, as exemplified by the foregoing, it is to be expected that continued improvements in thermal management materials and applications would be well-received by electronics manufacturers.
Accordingly, it is an objective of the present invention to provide an improved thermal management product that has a high degree of heat transfer efficiency and heat dissipation, that is conformable to the particular application, and that is simple to use and manufacture.